At a computer center etc, such a mode is known that a copy of a database (which is abbreviated to DB) used by the computer center is created in, e.g., a sub-computer center installed in a different location in preparation against an emergency such as occurrence of a disaster. Further, for instance, such a mode is also known that with an expansion of tasks etc, the database used by a main computer etc is copied, and a new task is carried out in such a way that a computer (sub-computer) different from the main computer uses the copied database (which is referred to as a replica DB).
Known as a method of creating the replica DB is a method of acquiring, e.g., a file (journal file) of update differential data (which are termed journals) given when updating the DB used by the main computer and transferring the acquired journal file to the sub-computer. The sub-computer extracts the update differential data given when updating the DB that are contained in the journal file, and reflects the update differential data in the replica DB used by the sub-computer, thereby ensuring the latest property of the replica DB.
If there exists a plurality of DBs used by the main computer, the main computer updates the plurality of DBs with one transaction, and a matching property between the plurality of DBs used by the main computer is assured by the transaction. The terminology “transaction” is defined as a single (isolated) work-unit (in a database environment) into which a plurality of related processes are aggregated, and the processes managed as the transaction result in “all gets successful” or “all gets into failure”.
For example, “sales DB” and “stock DB” are assumed as the plurality of DBs used by the main computer. If the matching property between “sales DB” and “stock DB” is assured by the transaction, a sales numerical value managed in “sales DB” rises as a sales count increases, while a stock numerical value managed in “stock DB” decreases at the same timing as the sales numerical value rises.
The matching property between “sales DB” and “stock DB” can be assured also by the transaction in a mode of transferring the journal file between the main computer and the sub-computer as described above. For instance, the main computer acquires the journal file by aggregating the journals of the plurality of DBs into one journal file and transfers the journal file to the sub-computer. The sub-computer may also aggregate the transferred journals into one transaction in the same way as the main computer does, and may reflect the transaction in the plurality of replica DBs.
Thus, also in the sub-computer using the plurality of replica DBs, the matching property between the replica DBs is assured by the transaction, and hence a task of referring to the replica DB can be operated even in the midst of performing the reflecting process in the replica DB.
It is to be noted that the following patent documents exist by way of the documents of the prior arts containing descriptions of technologies related to the technology, which will be discussed in the present specification.